20 times 9 is 180, but what is the answer if both 20 and 9 are negative numbers? Here we will determine if the answer to negative 20 times negative 9 is positive 180 or negative 180.
There are many different ways to explain and determine if the answer to negative 20 times negative 9 is -180 or +180 using mathematical terms such as additive inverse and mathematical laws like the Distribute Law.
We will take a different approach - process of elimination: We will simply test if -180 is the correct answer using basic algebra.
We will test if -180 is correct by setting up the equation negative 20 times negative 9 equals negative 180, and then simplifying the equation to see if it is true.
(-20) (-9) = (-180)
Divide both sides of the equation by (-9) :
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| = |
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The numerator and denominator on the left side both have (-9) which even each other out and can be removed:
| (-20) = |
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The numerator and denominator on the right side both have a minus sign (-) which even each other out and can be removed:
| (-20) = |
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A numerator of 180 and denominator of 9 on the right side is the same as 180 divided by 9 which is 20. Now we end up with this untrue equation:
(-20) = (20)
-20 is NOT equal to 20, thus we have proven that negative 20 times negative 9 is not equal to -180. The answer must therefore be 180:
-20 x -9 = 180
The above applies to all math problems where you multiply two negative numbers. Multiplying two negative numbers such as negative 20 times negative 9 will always have a positive answer.
Negative Times Negative Calculator
Here you can multiply another two negative numbers together.
What is negative 20 times negative 10?
Here is the next problem on our list that we have explained and calculated.
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